Method and apparatus for plasma generation

ABSTRACT

In a simple method and device for producing plasma flows of a metal and/or a gas electric discharges are periodically produced between the anode and a metal magnetron sputtering cathode in crossed electric and magnetic fields in a chamber having a low pressure of a gas. The discharges are produced so that each discharge comprises a first period with a low electrical current passing between the anode and cathode for producing a metal vapor by magnetron sputtering, and a second period with a high electrical current passing between the anode and cathode for producing an ionization of gas and the produced metal vapor. Instead of the first period a constant current discharge can be used. Intensive gas or metal plasma flows can be produced without forming contracted arc discharges. The selfsputtering phenomenon can be used.

TECHNICAL FIELD

The present invention relates to methods and apparatus for generatingplasma flows and in particular metals plasma flows obtained bydischarges in crossed electric and magnetic fields.

BACKGROUND OF THE INVENTION

Electrical discharges in crossed fields (EXB discharges) attract muchattention due to their importance for science and technology. In scienceEXB discharges are important in the field of plasma physics and cosmicphysics. In technology EXB discharges are used in devices forthermonuclear fusion, in vacuum technology such as in vacuum pumps,vacuum measurements, for coating work pieces using e.g. magnetronsputtering, ion plasma accelerators, and as plasma emitters in ionsources.

The motion of charged particles in stationary crossed fields andquasi-stationary EXB discharges have been studied since 1921, see thearticle by A. W. Hull, “The effect of a uniform magnetic field on themotion of electrons between coaxial cylinders”, Phys. Rev. 18, 1921, pp.31-57, and by H. C. Early, W. G. Dow, “Supersonic Wind at Low PressuresProduced by Arc in Magnetic Field”, Phys. Rev. 79, 1950, p. 186. Suchdischarges could be classified according to different parameters such asgas pressure, strength and configuration of the magnetic field used,electrode configuration etc. For the purposes herein these dischargesare best classified according to the intensity or generally thebehaviour of the discharge or driving current.

According to this classification using the driving current,quasi-stationary discharges in crossed fields could be divided in twoclasses: low intensity and high intensity current discharges. It isnecessary to note that the transition current depends on manyparameters, in particular on the dimensions of the apparatus used, andcan vary for hundreds of amperes. Low intensity current discharges incrossed fields could be called such discharges which produce a plasmainside a magnetic configuration with a density less than 10¹⁸ m⁻³ andhigh intensity current discharges could be called such discharges whichproduce a plasma having a density of more than 10¹⁸ m⁻³, the plasmadensity defined as the number of particles per unit volume.

Low intensity current discharges in crossed fields are widely used invacuum technology such as in vacuum pumps, for coating work pieces, e.g.in magnetron sputter deposition. Typical discharge devices are Penningcells and cylindrical and planar DC-magnetrons. The low driving currentresults in a low-density plasma, less than 10¹⁸ m⁻³ as indicated above.

High intensity current discharges have been mostly used for generatingdense plasma for the goals of thermonuclear fusion. Typical dischargedevices include Homopolar I, Ixion and F I devices. The typical plasmadensity is about 10¹⁸-10²³ m⁻³.

The second important characteristic of discharges in crossed fields isthe voltage drop between the electrodes.

For a low intensity driving current the rate of neutral gas ionizationis low and balances the plasma losses to form an equilibrium plasmadensity at a low level. The electrical resistance of the anode-cathodegap is high resulting in a high anode-cathode potential drop. As soon asan opposite process becomes energetically possible a strongly enhancedionization process should arise.

Two methods have been described for plasma ionization in systems usingwith discharges in crossed electric and magnetic fields. Their practicalapplicability depends on system dimensions and the strength of themagnetic field. The method generally accepted in systems of sufficientlylarge dimensions using a strong magnetic field is the so called“Rotating Plasma Approach”. This approach is based on the fact that theelectric field penetrates into the plasma and that the plasma ismagnetized, see B. Lehnert, “Rotating Plasmas”, Nuclear Fusion 11, 1971,pp. 485-533. Another approach is based on fact that the electric fieldis concentrated preferably near the cathode of the discharge. Thisapproach is used for processes in systems using a low magnetic field andnon-magnetized ions. This approach could be called e.g. “SecondaryElectron Approach”, see B. S. Danilin and B. K. Sirchin, MagnetronSputtering Systems, Moskva, Radio i Sviaz, 1982. As will be obvious fromthe following this invention deals with both kinds of systems andtherefore both plasma approaches will be used.

Alfvén has postulated, see H. Alfvén, “On the Origin of the SolarSystem”, Clarendon Press, Oxford, 1954, that a strongly enhancedionization process should arise when the mutual plasma-neutral gasvelocity reaches the critical value v_(c), the Alfvén limit, given by

v _(c)=(2e¢ _(i) /m _(i))^(1/2)

where ¢_(i) is the ionization potential, e is the charge of the electronand m_(i) is the ion mass.

For devices having a low sputtering rate and low plasma losses itresults in an anode-cathode voltage drop limitation during the startingperiod of the discharge. For devices having a high sputtering rate itresults in an anode-cathode voltage drop limitation during all of thedischarge time. The voltage drop or critical voltage V_(c) is given by

V _(c) =Cv _(c) B

where C is a constant and B is the strength of magnetic field in thedischarge device. In the case of a high sputtering rate, the ionizationpotential ¢_(I) of the sputtered atoms creates the metal vapor. It meansthat the discharge voltage has to depend on the sputtering cathodematerial.

This phenomenon was demonstrated both by investigation of plasma motionthrough a neutral gas and by experiments with planar magnetronsputtering devices, see U. V. Fahleson, “Experiments with Plasma Movingthrough Neutral Gas”, Physics Fluids, Vol. 4, 1961, pp. 123-127, and D.V. Mozgrin, I. K. Fetisov, and G. V. Khodachenko, “High-CurrentLow-Pressure Quasi-Stationary Discharge in a Magnetic Field:Experimental Research”, Plasma Physics Reports, Vol. 21, No. 5, 1995,pp. 400-409. In the latter publication the high current, low voltagedischarge in a magnetron magnetic configuration is called as a“high-current diffuse regime”.

It means that the transition from a low intensity current EXB dischargeto a high intensity current discharge has to be followed by a decreaseof the discharge voltage. Typical anode cathode potential drops for lowintensity current, quasi-stationary discharges are in the range of about10-0.3 kV and for high intensity current discharges in the range ofabout 300-10 V.

If quasi-stationary discharges are implemented in magnetron sputteringdevices, in a first regime effective cathode sputtering is obtained buta low ionization rate of the sputtering gas and metal vapor. In a secondregime an opposite state occurs having a low sputtering rate but a highionization rate of the sputtering gas. Thus, it can be said that it isimpossible to generate, by a separate low intensity currentquasi-stationary discharge, or by a separate high intensity currentdischarge in crossed fields, highly ionized metal plasma fluxes.

The devices using EXB discharges can operate for a short time in thetransient, i.e. the non-quasi-stationary, regime. In this regime it ispossible to overcome the Alfvén limit of discharge voltage as well forhigh current discharges, see the article by B. Lehnert cited above. Highcurrent, high voltage non-quasi-stationary discharges occur in magnetronsputtering devices and are very important for magnetron sputteringapplications because those discharges allow obtaining a fully ionizedimpermeable plasma in the magnetron magnetic configuration. But, as willbe shown hereinafter, if transient discharges are implemented inmagnetron sputtering devices by either high intensity current dischargesor by low intensity current discharges it is impossible to generatehighly ionized intensive metal plasma fluxes.

Metal plasma fluxes can be produced by low current quasi-stationary EXBdischarges in a magnetron configuration for sputtering atoms in amoderate pressure, of e.g. 1-100 mTorr, and with a low-density plasma.In this case the plasma is produced by an RF-induction coil mounted inthe deposition chamber. The electron density produced in inductionplasmas is about 10¹⁷-10¹⁸ m⁻³.

This method of coating work pieces has important implications for thefilling of high-aspect-ratio trenches and vias encountered inmicroelectronic fabrication processes as well as in sputtering magneticmaterials and modifying the properties of thin films by energetic iondeposition, see J. Hopwood and F. Qian, “Mechanisms for highly ionizedmagnetron sputtering”, J. Appl. Phys. 78 (12), 15 Jul. 1995, pp.758-765.

The drawbacks of this method of metal plasma production include thecomplexity of the RF-ionization technique and the high pressure of thesputtering gas required for producing the low-density plasma. The highpressure of the sputtering gas is required because of the high energyconsumption necessary for producing a low-density plasma.

The discharges in crossed fields could be implemented by simpletechniques and within an extremely wide range of operating pressures:from 10⁻¹¹ up to 10² Torr. Low-pressure magnetron discharges, up to 10⁻⁵Torr, can be achieved because of the selfsputtering phenomenon, see forexample S. Kadlec and J. Musil, “Low pressure magnetron sputtering andselfsputtering discharges”, Vacuum, Vol. 47, pp. 307-311, 1996. Thismethod of coating work pieces has important implications for the etchingof surfaces by metal ions for increasing the adhesion of depositedlayers and for the filling of high-aspect-ratio trenches and viasencountered in microelectronic fabrication.

The currents necessary for generating a dense plasma and sustaining itby high intensity current EXB discharges are large enough for cathodespots, and possibly also for anode spots, to be formed at the coldelectrode surfaces. Devices having such electrodes should therefore havea natural tendency of forming spoke-shaped azimuthal plasmainhomogeneities, arc discharges, see B. A. Tozer, “Rotating Plasma”,Proc. IEEE, Vol. 112, 1965, pp. 218-228. Such conditions are stronglypronounced in all types of devices during the starting period of thedischarges where a large driving current is needed for neutral gasburn-out.

Having cold electrodes and neutral-plasma phenomena in mind, theexperiments on plasma spoke formation can be summarized as follows:

a. In the Homopolar III experiments it was found that during thestarting period the discharge current was confined to a set of about 10to 12 narrow radial spokes, arcs, rotating with the plasma. See W. R.Baker, A. Bratenal, A. W. De Sliva, W. B. Kunkel, Proc. 4^(th) Int.Conf. Ionization Phenomena in Gases 2, Uppsala 1959, North-HollandPublishing Comp., Amsterdam, p. 1171, and W. B. Kunkel, W. R. Baker, A.Bratenahl, K. Halbach, “Boundary Effects in Viscous Rotating Plasmas”,Physics Fluids, Vol. 6, 1963, pp. 699-708.b. In the Leatherhead Homopolar device having a negative polarity one ortwo spokes were observed to arise during the initial breakdown of thedischarge. They were soon smeared out to form spirals with an increasingvelocity in the outward radial direction, see P. B. Barber, M. L.Pilcher, D. A. Swift, B. A. Tozer, C. r. de la Vi^(e) conferenceinternationale sur les phenomènes d′ionization dans le gas 2, Paris,1963, p. 395.c. In the Kruisvuur I device a single eccentric structure rotatingaround the axis with a velocity close to E/B was observed, see C. E.Rasmussen, E. P. Barbian, J. Kistemaker, “Ionization and current growthin an ExB discharge”, Plasma Physics, Vol. 11, 1969, pp. 183-195.

From the experiments mentioned above and others, arc formation isclearly seen to be connected with the starting period of the highintensity current EXB discharges in most devices.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide methods andapparatus allowing production of intensive, preferably gas or gas-metalor most preferably metal plasma flows.

The problems, which the invention thus intends to solve, comprise:

1. How to produce intensive, preferably gas or gas-metal or preferablymetal plasma flows by ionization of gas and metal vapor produced usingplanar magnetron sputtering cathodes by a simple technique for producingdischarges in crossed fields.2. How to produce these plasma flows without forming contracted arcdischarges.3. How to provide pulsed discharges in crossed fields using theselfsputtering phenomenon.

Thus, generally in a method for producing a plasma flow successive lowand high intensity current quasi-stationary and non quasi-stationarydischarges in crossed electric and magnetic fields are used, the term“crossed fields” meaning “crossed electric and magnetic fields” herein.For producing the plasma a succession of discharges is thus used, i.e.pulsed discharges are used. The discharges that are well separated intime are defined to be quasi-stationary in the cases where at least themost important physical parameters, such as current and voltage, aresubstantially constant or slowly varying during most of the dischargetime, and are, if this condition is not fulfilled, non-quasi stationary.The plasma flow producing procedure can include the following steps:

1. A low intensity current, high voltage discharge in a magnetronmagnetic configuration is used for metal vapor production. The followingionization of vapor is obtained by a high intensity current, low or highvoltage discharge in the same magnetic configuration. The second,ionizing discharge starts immediately after the first one or with some,relatively small time delay. The parameters of the pulses and time delayof the second pulse are defined by the requirements imposed by the highionization of sputtered vapor blobs.2. The metal vapor can be produced by a direct current discharge, i.e.not by pulsed discharges. In this case the metal vapor produces acontinuous vapor flow out of the magnetic configuration where thedischarge is made. If ionizing pulses follow having a sufficientfrequency and driving current it is possible to produce a continuousmetal plasma flow having a modulated intensity.

The following basic schemes can be used:

1. The plasma can be produced in a magnetron magnetic configuration inwhich combined or successive low and high intensity currentnon-quasi-stationary discharges in crossed fields are used.2. The plasma can be produced in a magnetron magnetic configuration inwhich a low intensity current quasi-stationary discharge is combinedwith or followed by a high intensity current non-quasi-stationarydischarge, the discharges made in crossed fields.3. The plasma can be produced in a magnetron magnetic configuration inwhich combined direct current discharges and high currentnon-quasi-stationary discharges in crossed fields are used.4. The plasma can be produced in a magnetron magnetic configuration inwhich combined low intensity current non-quasi-stationary discharges andhigh intensity current quasi-stationary discharges in crossed fields areused.5. The plasma can be produced in a magnetron magnetic configuration inwhich combined successive low and high intensity currentnon-quasi-stationary discharges and high intensity currentquasi-stationary discharges in crossed fields are used.6. The plasma can be produced in a magnetron magnetic configuration inwhich combined high intensity current non-quasi-stationary dischargesand high intensity current quasi-stationary discharges in crossed fieldsare used.

The combinations of discharges in crossed electric and magnetic fieldsmentioned above made in a magnetron magnetic configuration allow theproduction of plasma flows of preferably gas or gas and metal or mostpreferably of a metal plasma flow. For quasi-stationary discharges thechoice of method can be based on the different efficiencies of the lowand high current intensity discharges for sputtering and ionization inthe different cases.

The discharges in crossed fields have, as has been mentioned above, anatural tendency of forming spoke-shaped azimuthal plasmainhomogeneities—arc discharges. The probability of the transition of anEXB discharge in magnetron type devices to a contracted arc dischargeincreases with an increasing driving current. In low current dischargesarcing occurs very rarely and it is possible to prevent the transitionto arc discharges by specially adapted arc suppression schemes in thedischarge power supply. In high current discharges there is a very highprobability of arc discharges being formed and solutions to the problemof suppressing arc formation using similar schemes are not efficient. Aswill be described herein, arc suppression can be achieved using a nowdiscovered phenomenon of dependence of arc formation on the plasmaconfinement properties of the magnetron magnetic configuration and onthe time between discharges. The balanced magnetron magneticconfiguration has relatively low plasma confinement properties.Therefore, for achieving efficient arc suppression, it is necessary touse a magnetic field having a high strength. In this case the plasmalosses caused by diffusion will decrease as B⁻² in the case of classicdiffusion or as a B⁻¹ in the case of Bohm diffusion, where B is thestrength of the magnetic field. It was found that for a balancedmagnetron magnetic configuration, in order to achieve efficient arcsuppression, it is necessary to have a magnetic field strength of theradial B component of about 0.07-0.3 T, the radial direction here takenas directions parallel to the substantially flat surface of the cathodeor target. Unbalanced and cusp-shaped magnetic configurations haveimproved plasma confinement properties; therefore, for effective arcsuppression it is sufficient to have a magnetic field strength of about0.04-0.3 T.

The plasma confinement properties of the magnetic configuration stronglyaffect the lower limit of the operating pressure used in the space atthe cathode. It was found that for improving the plasma confinementproperties the operating pressure of the EXB discharge should bedecreased. For a certain operating frequency a gas atmosphere isrequired only for starting the discharge. After the starting period itis possible to initiate the discharge by the residual plasma densityleft from the previous pulse. In this case metal vapor is produced byusing the selfsputtering phenomenon and the plasma in the magnetic trapcontains primarily ions of the target metal. The plasma flow from themagnetic trap contains preferably ions of the target metal as well.

Generally, it can be said that the primary concept of the methoddescribed herein is to combine the magnetic configuration havingimproved plasma confinement properties with low and high intensitycurrent quasi-stationary discharges and non-quasi-stationary dischargesor DC and high intensity current discharges for generating stable andintensive plasma flows. Low and high intensity current quasi-stationarydischarges and non-quasi-stationary discharges are produced one afteranother with a repeating frequency exceeding a minimal critical valuedepending on the plasma confinement properties of the magnetic trap. Inthe case of DC sputtering discharges, a high rate of ionization of gasand metal vapor is produced by a periodic repetition of the ionizingdischarges.

The methods and devices described herein can be used both in the“Rotating Plasma Approach” and the “Secondary Electron Approach”mentioned above.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe methods, processes, instrumentalities and combinations particularlypointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

While the novel features of the invention are set forth withparticularly in the appended claims, a complete understanding of theinvention, both as to organization and content, and of the above andother features thereof may be gained from and the invention will bebetter appreciated from a consideration of the following detaileddescription of non-limiting embodiments presented hereinbelow withreference to the accompanying drawings, in which:

FIGS. 1 a-1 f are schematic views of different magnetron magneticconfigurations used in magnetron sputtering, in which

FIG. 1 a is a view of a first type of an unbalanced magnetron magneticconfiguration,

FIG. 1 b is a view of a balanced magnetron magnetic configuration,

FIG. 1 c is a view of a second type of an unbalanced magnetron magneticconfiguration,

FIGS. 1 d and 1 e are views illustrating the magnetic configurationcreated by permanent magnets placed behind the target and anelectromagnetic coil placed in front of the target,

FIG. 1 f is a view of a cusp-shaped magnetic configuration,

FIG. 1 g is a view from above of a magnetic configuration typical ofmagnetrons having a rotating magnet,

FIG. 1 h is a schematic cross-sectional view showing the magnetic forcelines in the magnetic configuration of FIG. 1 g,

FIGS. 2 a and 2 b are schematic diagrams illustrating limits between lowand high current discharges of the quasi-stationary andnon-quasi-stationary type respectively,

FIGS. 3 a and 3 b are schematic diagrams of current and voltage pulsesrespectively as functions of time for sputtering and ionizing dischargesin crossed fields,

FIG. 4 is a schematic diagram of periodic current pulses of the kindillustrated in FIG. 3 a as a function of time,

FIG. 5 is a schematic diagram similar to that of FIG. 4 showing analternative shape of the current pulses,

FIG. 6 a is a schematic diagram showing a constant current forsputtering discharge,

FIG. 6 b is a pulsed ionizing discharge that is combined with thesputtering discharge,

FIG. 7 a is a schematic diagram of the conductivity and plasma densityas a function of time in a plasma confinement region,

FIG. 7 b is a schematic diagram substantially identical to that of FIG.4 showing the driving current pulses for producing the conductivity andplasma density of FIG. 7 a,

FIG. 8 a is an electrical circuit diagram of a device for producing ametal vapor and the ionization thereof, the device having two pulsedpower supplies connected in parallel,

FIG. 8 b is a diagram similar to that of FIG. 8 a of a device includinga single pulse power supply having a variable impedance,

FIG. 8 c is a diagram similar to that of FIG. 8 a of a device having asingle pulsed power supply combined with a DC power supply,

FIG. 9 is a detailed electrical circuit diagram corresponding to thediagram of FIG. 8 a,

FIG. 10 is a detailed electrical circuit diagram corresponding to thediagram of FIG. 8 b,

FIG. 11 is a detailed electrical circuit diagram corresponding to thediagram of FIG. 8 c,

FIG. 12 a is a schematic cross-sectional view of a plasma sourceutilizing discharges in crossed electric and magnetic fields for gas orgas and metal or metal plasma production, corresponding to the secondtype of unbalanced magnetron magnetic configuration shown in FIG. 1 c,and

FIG. 12 b is a schematic view similar to that of FIG. 12 a illustratinga plasma source utilizing discharges in crossed electric and magneticfields for gas or gas and metal or metal plasma production,corresponding to the types of magnetron magnetic configurations shown inFIGS. 1 d and 1 f.

DETAILED DESCRIPTION

The magnet configurations of magnetron sputtering cathodes preferablyused in the conventional art for a magnetic field strength of up to 0.1T are illustrated in FIGS. 1 b-1 f. Thus, in FIG. 1 b a balancedmagnetron magnetic configuration is shown whereas in FIGS. 1 a and 1 cunbalanced magnetron magnetic configurations are shown. The altering ofthe magnetic field configuration is here made by altering theconfiguration of the permanent magnets in the magnetron source.

Thus, in the schematic diagram of FIG. 1 a a first type of an unbalancedmagnetron magnetic configuration is illustrated. The magnetronsputtering cathode 1 is a substantially flat body of the material to besputtered and can have the shape of circular disc or a rectangularplate. At the rear or bottom surface of the cathode a permanent magnetassembly is illustrated comprising an outer magnet 2 and a centralmagnet 3, the central magnet located at the center of the rear side ofthe cathode and the outer magnet located at the edge of the rear side ofthe cathode. The lines having arrows show the direction of magneticforce lines. The strength of the central permanent magnet 3 is selectedto be larger than the strength of the outer magnet 2 so that among themagnetic field lines 4, generally going from the north poles to thesouth poles of the magnets, some field lines extend only between thepoles of the central permanent magnet.

In the view of a balanced magnetron magnetic configuration in FIG. 1 bit is seen to have substantially the same set-up as the magnetronconfiguration as in FIG. 1 a. However, the strength of the centralmagnet is selected to be equal to the strength of the outer magnet sothat substantially all magnetic field lines extend between a pole of thecentral magnet 3 and a pole of the outer magnet 2. The shaded area inthe figure is the area of plasma confinement and also the area in whichthe power dissipation of the discharge occurs.

In the schematic of FIG. 1 c a view of a second type of an unbalancedmagnetron magnetic configuration is illustrated, in which the strengthof the permanent magnets is selected in still another way. Here, somefield lines extend between the poles of the outer magnet, the fieldlines starting or ending at the central magnet all having their otherends at the outer magnet.

The unbalanced configurations as shown in FIGS. 1 a and 1 b areclassified as Type I or Type II respectively, see B. Window and N.Savvides, “Charged particle fluxes from planar magnetron sputteringsources”, J. Vac. Sci. Technol, A 4(2), 1986, pp. 196-202.

An alternative way to accomplish different magnetic configurations is touse an external, preferably toroidal, magnetic coil, see I. Ivanov, P.Kazansky, L. Hultman, I. Petrov, and J-E. Sundgren, “Influence of anexternal axial magnetic field on the plasma characteristics anddeposition conditions during direct current planar magnetronsputtering”, J. Vac. Sci. Technol., A 12(2), 1994, pp. 314-320. Thus, inthe views of FIGS. 1 d, 1 e and 1 f magnetic configurations created bypermanent magnets 2, 3 placed behind the target 1 and an electromagneticcoil 5 placed in front of the target are shown. In FIGS. 1 d and 1 e thecoil has a diameter larger than the diameter of the target. The arrowsshow the direction of the magnetic field. In FIG. 1 f a cusp-shapedmagnetic configuration is shown in which the coil 5 has a diametersmaller than the diameter of the target and of the outer magnet. Theelectromagnetic coil 5 has a height b_(coil), i.e. the extension thereofin a direction perpendicular to the plane of the cathode 1, and an innerdiameter D_(coil). h and D are generally the height and diameter of theregion of plasma confinement, the power dissipation of the dischargeoccurring in this region. The shape of the plasma confinement region canroughly be considered as a cylinder, having a diameter D and a height h,for a planar circular cathode 1 or as rectangular parallelepiped for aplanar rectangular cathode. In the latter case D is the smallestdimension of cathode and the smallest dimension of the base surface ofthe parallelepiped and h is the height of the parallelepiped.

Depending on the direction of the electric current in the coil 5, itsfield can be used for assisting either the outer pole 2 or the centerpole 3 of the permanent magnets as illustrated by FIGS. 1 d and 1 e.This technique provides a plasma density inside the plasma confinementregion of about 10¹⁶ m⁻³ and provides for means of varying the ion fluxat the cathode or substrate by more than one order of magnitude. Butstill, the ionization rate is less than 10%. Therefore, the variationonly of magnetic field strength and its geometry cannot give asputtering magnetron cathode acting as a metal plasma source having ahigh equivalent current.

The cusp-shaped magnetic configuration of FIG. 1 f has been used forproduction of a dense plasma by high current quasi-stationary dischargesgenerated by periodic pulses having a low frequency less than 10 Hz. Twoaxially symmetric electromagnetic coils having opposite currentdirections created the cusp shaped magnetic configuration, see thearticle by D. V. Mozgrin et al. cited above.

The configuration including a cusp-shaped magnetic field created bypermanent magnets and an electromagnetic coil as illustrated by FIG. 1 fwill now be considered. There, the electromagnetic coil 5 is placed at adistance h=aD, h also being the height of the plasma confinement region,from the exposed, front surface of the sputtering magnetron cathode 1,where a is a coefficient having a value in the range of 0.1-1 and D asabove is the diameter of the confinement region and thus the diameter ofthe cathode for a circular shape thereof or equal to the smallestdimension of the cathode for a rectangular planar shape thereof. Theinner dimension of the electromagnetic coil 5, for a circular shapethereof, is D_(coil)=bD, where b is a coefficient having a value in therange of 0.4-1.4 and D_(coil) is the inner diameter. The innerdimensions of the coil for a rectangular shape thereof are D_(coil) andH, where D_(coil)=bD, D_(coil) is the smallest inner dimension of thecoil and b is a coefficient having a value in the range of 0.4-1.4. Theheight b_(coil) of the electromagnetic coil 5 is equal to b_(coil)=cD,where c is a coefficient having a value in the range of 0.3-3.

The magnetic configuration typical of magnetrons having a rotatingmagnet is illustrated in FIG. 1 g, see also U.S. Pat. No. 5,252,194 forRichard A. Demaray et al. The permanent magnets 2′ are positioned at thesputtering surface of the cathode 1 as shown in the figure. The magnetassembly 2′ rotates around the center of cathode parallel to the rearsurface thereof. The configuration of the magnetic force lines is seenin FIG. 1 h. The configuration has a characteristic dimension D.

Generally, in the method described herein, magnetic configurations ofthe kinds illustrated in FIGS. 1 b, 1 c, 1 d, 1 f and 1 g can be used.However, in the method discussed in the following the configurationincluding an unbalanced magnetron configuration as illustrated by FIG. 1c will be preferably considered.

Quasi-stationary discharges generated in balanced sputtering magnetrondevices, such as in that shown in FIG. 1 b, are characterized by anefficient cathode sputtering but a low ionization rate of the sputteringgas and metal vapor for low current discharges or by a low sputteringrate but by a very high ionization efficiency of the sputtering gas andmetal vapor for high current discharges. Hence, it can be said thatusing low or high current quasi-stationary discharges in crossed fieldsit is impossible to generate intensive, highly ionized metal plasmafluxes.

Conventional methods of increasing plasma fluxes for low direct currentmagnetron discharges are preferably based on improvement of the plasmaconfinement properties of the magnetron magnetic configuration. Thesemethods are obvious since the ionization efficiency in plasma largelydepends on the electron density. The plasma confinement could beimproved by increasing the magnetic field strength and/or by changes ofthe magnetic field configuration.

In the diagrams of FIGS. 2 a and 2 b the transition from the lowintensity current region to the high intensity current region is shown.The diagram of FIG. 2 a shows the voltage as a function of the dischargecurrent for the case of quasi-stationary discharges. The transitioncurrent I_(transition) corresponds to the discharge or driving currentvalue when the high voltage, initial discharge continues to a lowvoltage discharge. When the plasma density is sufficiently high, what isachieved for a sufficiently high driving current, to establish nearlyisotropic and equal ion and electron temperatures, the component E_(∥)of the electric field parallel to the magnetic B-field becomes smallcompared to the transverse component E_(tr) thereof. The plasma thenobeys the isorotation law according to which the angular velocitybecomes uniform along a magnetic field line and the plasma rotates as awhole, a so called rotating plasma, see the article by B. Lehnert citedabove. For low plasma densities, i.e. for a low driving current,quasi-stationary discharges also exist in which the longitudinalelectric field E_(∥) cannot be neglected and the isorotation law becomesinvalid. Recent systems include Penning cells as well as magnetronsputtering cathodes powered by direct current discharges. Theisorotation phenomenon defines the limit between the low intensity andhigh intensity current quasi-stationary discharges. Practically, thetransition from the low to the high current discharges results in a dropof the discharge voltage down to values corresponding to the AlfvénLimit.

The solid line and the dashed line in the diagram of FIG. 2 b show themetal deposition rate and the gas plasma flux intensity respectively asfunctions of the driving current for the case of non-quasi-stationarydischarges. In the low intensity current range, i.e. in the first tworegions I and II, the deposition rate first increases, in the region I,and then becomes constant, in the region D, for an increasing drivingcurrent. In the high intensity current range, i.e. in the regions IIIand IV, the deposition rate first decreases, in the region III, and thenbecomes constant, in the region IV, for an increasing driving current.For non-quasi-stationary discharges this behavior of the deposition ratecan be explained by the now discovered phenomenon of differentdependencies of the intensity of gas and metal plasma production on theintensity of the discharge or driving current in a magnetron magneticconfiguration. It is found that for an increasing intensity of thedischarge current the intensity of the metal plasma production initiallyincreases up to certain level and thereafter it is strongly decreasing,see the solid line of the diagram of FIG. 2 b. The intensity of the gasplasma flux increases all the time for an increasing intensity of thedischarge current.

Explanation of this phenomenon could be done by the phenomenon ofgeneration of a high intensity current of secondary electrons emittedfrom the cathode by bombarding it by high intensity ions derived fromthe discharge driving current. Secondary electrons to be accelerated upto the high cathode voltage drop efficiently ionize gas and vapor bycollisions between electrons and neutral particles and by the phenomenonof destabilization of the plasma of gas and sputtered vapor near thecathode. It results in excitation of plasma instabilities of a kinetictype that in turn strongly increase the effective collision frequencyand thereby effectively heat the bulk of plasma electrons. According toP. Gopalraja and J. Foster, “Nonlinear wave interaction in a magnetronplasma”, Applied Physics Letters, Vol. 77, No. 22, November 2000, pp.3526-3528, the intensive beam of high-energy secondary electrons candrive beam-plasma-type instabilities.

Both the high electron density near the cathode and the high temperatureof the electrons result in a phenomenon of efficient vapor ionization inthe region of the cathode voltage drop. To be ionized in the region ofthe cathode voltage drop the gas and metal ions are returned back to thecathode surface by the electric field existing in that region, what isthe self sputtering phenomenon. It results in a sharp reduction of thedeposition rate if the discharge driving current exceeds a certainvalue. This value is shoved in FIG. 2 b as the line for the currentI_(transition). This phenomenon is most obvious for cathodes producedfrom metals having low sputtering yields. At the opposite side of thecathode voltage drop region the sputtering and/or reactive gases arelocated, which are extremely efficiently ionized by the same phenomenon.For example, for a circular planar magnetron sputtering cathode oftitanium and having a diameter of 150 mm, operating in thenon-quasi-stationary regime for the following parameters: dischargecurrent 1400 A and discharge voltage 500-600 V, the deposition rate isabout zero and the ratio of Ar⁺-current to Ti⁺-current is 1:10 000. Thisphenomenon allows the design of a plasma source operating as a gasplasma source or as a gas-metal plasma source or as a metal plasmasource which is very promising not only for PVD but also for CVDapplications.

If the magnetron sputtering cathode operates only in the region of highintensity current non-quasi-stationary discharges or the region ofcombined high intensity current non-quasi-stationary discharges and highintensity current quasi-stationary discharges in crossed fields itproduces preferably a gas plasma with a low contamination of a plasma ofthe cathode metal. If such discharges are used in combination with lowintensity current discharges, the system operates as a gas-metal ormetal plasma source, because the low current discharges allow the regionof the magnetron magnetic configuration above the charge separationlayer to be filled with metal vapor. This vapor is ionized together withthe gas by the high current discharges. It is obvious that the systemfor a proper operation as a gas-metal or metal plasma source requires aspecific timing of successive pulses and a specific choice of pulsedurations. I.e., the duration of the vaporizing pulses must not belarger than the time-of-flight of the vapor blob across the magnetronmagnetic configuration where the energy dissipation takes place.

The boundary between the low and high current non-quasi-stationarydischarges could be specified as follows. A low intensity dischargecurrent corresponds to the region where the deposition rate provided bythe metal of magnetron sputtering cathode is all the time increasing oris about constant for an increasing discharge current, see the regions Iand II respectively of the diagram of FIG. 2 b. A high intensitydischarge current corresponds to the region where the deposition rateprovided by the metal of the magnetron sputtering cathode is all thetime decreasing or is about constant for an increasing dischargecurrent, see the regions III and IV of the diagram of FIG. 2 b. Both thequasi-stationary and the non-quasi-stationary discharges have atransition from the low intensity current discharges to the highintensity current discharges provided that the power of the dischargesexceeds the burn-out power, see the article by B. Lehnert cited aboveand the published International patent application No. WO 98/40532, andthe corresponding driving current exceeds the burn-out current, see thelines for I_(transition) in the diagrams of FIGS. 2 a and 2 b. Referencecan also be made to Karol Macák, Vladimir Kouznetsov, Jochen Schneider,Ulf Helmersson, Ivan Petrov: “Ionized sputter deposition using anextremely high plasma density pulsed magnetron discharge”, J. Vac. Sci.Technol., A 18(4), July/August 2000, pp. 1533-1537.

In the case of discharges made in crossed electric and magnetic fieldsin magnetron sputtering cathode devices, for the calculation of theburn-out current the phenomenon of plasma turbulization has to be takeninto account. It is necessary to notice that a low level of plasmaturbulization can be obtained already in the low intensity dischargecurrent, see FIG. 2 b, region II and the portion of region I near regionII, but it result in a low level, less than 10%, ionization rate of thesputtered vapor. This technology is already used practically incommercial SIP (Self Ionized Plasma) deposition sources, available fromApplied Materials, see the Internet document Barry L. Chin, G. Yao, P.Ding, J. Fu and L. Chen, “Barrier and Seed Technologies for Sub-0.10 μmCopper Chips”, Semiconductor International, May 2001,http://www.semiconductor.net/semiconductor/issues/2001/200105/04six0105m. . . .

The advantage of the methods and devices described herein residesparticularly in the possibility to produce highly ionized, up tocomplete ionized, metal plasma flows.

In the diagrams of FIGS. 3 a and 3 b the current and voltage of pulsesapplied between the cathode 1 and the anode, not shown, the anodegenerally comprising the walls of the sputtering chamber, areillustrated as functions of time for achieving sputtering and ionizingdischarges in crossed fields with a high efficiency. There, I is thedischarge or driving current and U is the discharge voltage. The pulsescomprise a first, long time interval, with a high voltage U₁ and lowcurrent I_(I), for achieving a sputtering discharge followed by a secondinterval in which an ionizing discharge is generated. In the secondinterval, which is considerably shorter than the first interval, theapplied voltage U₂ is low and the current I₂ is high. t₁ is the starttime of the sputtering discharge interval and t₂ is the time when thesputtering discharge interval ends. t₃ is the time when the ionizingdischarge starts which is here equal to t₂. t₄ is the time when theionizing discharge period ends. t₂ is as well the time when the front ofthe sputtered vapor blob reaches the boundaries of the power dissipationregion.

FIG. 4 is a diagram of the current of the pulses as functions of timeschematically showing how the pulses are repeated with a pulse repeatingperiod T.

FIG. 5 is a diagram similar to that of FIG. 4 but here, according to asecond embodiment, the time intervals of the sputtering and ionizingdischarges are separated by a short time interval of length Δ=(t₃−t₂)during which no voltage is applied.

FIGS. 6 a, 6 b are diagrams of the current as a function of timeillustrating how the pulses can be applied according to a thirdembodiment. In this diagram of FIG. 6 a a constant current I_(DC) isshown used for achieving the sputtering discharge. This constant currentis combined with a pulsed ionizing discharge as shown in FIG. 6 b, thedriving current I₂ during the pulses of the ionizing discharges beingconsiderably higher than the constant current. t₃ is the start time ofthe intervals of the ionizing discharges beginning and t₄ is the timewhen the ionizing discharges end.

FIG. 7 a is a diagram showing the conductivity δ and plasma density n asa function of time in the plasma confinement region. The driving currentpulses are shown in the diagram of FIG. 7 b as a function of time. Thefilling of the plasma confinement region by metal vapor can be producedby a DC discharge, see FIGS. 6 a, 6 b, or by pulsed low currentdischarges, as in FIGS. 3 a, 3 b, 4 and 5. In FIG. 7 a δ _(max) andn_(max) are the maximal conductivity of the discharge gap and the plasmadensity in the plasma confinement region produced by the ionizingdischarge respectively and δ_(min) and n_(min) are the minimalconductivity and the plasma density respectively for the case when thesputtering magnetron discharge can be initiated without the presence ofa sputtering gas. T_(max) is the maximal time between ionizing pulseswithin which it is possible to initiate the sputtering magnetrondischarges without the sputtering gas.

In tests of the magnetic configurations described in conjunction withFIGS. 1 a-1 g it was found that:

1. The strength and geometry of the magnetic field which define theplasma confinement properties strongly affect the transition of a lowcurrent EXB discharge into a high current EXB discharge or possibly intoa contracted arc discharge. The configurations useful, and thuspreferred here, for a stable operation without any contracted arcformation in low and high current quasi-stationary discharges aremagnetic configurations are those schematically illustrated in FIGS. 1b, 1 c, 1 d, 1 f and 1 g as has been indicated above.2. Plasma inhomogeneities like contracted arcs prevail during aquasi-stationary holding mode in systems having large plasma losses,i.e. low confinement properties.3. The process of contracted arc formation depends on the initial plasmadensity in the magnetic trap in the start period of the ionizing highcurrent discharge in crossed fields.4. For application of discharges in crossed fields to magnetronsputtering cathodes a most important phenomenon comprises the formationof cathode spots. It is a well known fact that cathode spots are formedif the field emission of electrons from the cathode is replaced by athermoelectric emission, resulting in an explosive electron emission andtransformation of the cathode metal, at sharp inhomogeneities on thecathode surface, into dense plasma blobs. These plasma blobs form plasmainhomogeneities, which are centers of concentrated arc formation. It isobvious that in order to reduce the probability of explosive electronemission it is necessary to remove the sharp inhomogeneities from thecathode surface. It was found that the direct current, low intensityquasi-stationary and low intensity non-quasi-stationary discharges areefficient methods of cathode surface polishing and, in contrast, highcurrent intensity quasi-stationary and non-quasi-stationary dischargesare very efficient methods of roughening the cathode surface. Therefore,if only high current intensity, quasi-stationary and especiallynon-quasi-stationary discharges are used for plasma production theformation of concentrated cathode arcs increases with the duration ofthe deposition process. If double-pulse discharges or a combination ofan applied direct or constant current and high current pulsed dischargesare used the formation of concentrated cathode arcs is stronglysuppressed. Thus, the contracted arc discharges can be suppressed bysuitably selected arc suppression schemes incorporated in the plasmadriving power supply.

The phenomenon mentioned above show that in order to avoid formation ofarc discharges during high current discharges it is necessary to startthe high current discharge with a sufficient initial conductivity of thedischarge gap. It can be achieved by having a sufficient plasma densityin the magnetic trap in the start period of the discharge, see FIG. 7,and maintaining low plasma losses during the discharge.

It was found that in terms of the electric, magnetic and time parametersof the discharge device used in order to avoid arc formation, it isnecessary to use the following values of the parameters:

a. The magnetron magnetic configuration of the balanced type, see FIG. 1b, has to have a maximum radial strength of the magnetic field of0.07-0.3 T at the sputtering surface of cathode, the radial directionstaken parallel to the plane of the front surface of the target orcathode.b. The magnetron magnetic configurations of the unbalanced type, seeFIGS. 1 c and 1 d, have to have a maximum radial strength of themagnetic field of 0.04-0.3 T at the sputtering surface of cathode.c. The cusp-shaped axis-symmetric magnetic configuration, see FIG. 1 f,has to have a maximum radial strength of the magnetic field of 0.04-0.3T at the sputtering surface of cathode. The cusp-shaped magneticconfiguration used is created by a balanced magnetron magnetic fieldproduced by a permanent magnetic system combined with the magnetic fieldfrom a toroidal electromagnetic coil having a relatively small diameter.d. Low and high current discharges have to be periodically repeated andfollowing one after another in time with a pulse repetition frequency fof the magnitude of order of 100 Hz-20 kHz, in particular with afrequency of 0.5-2 kHz, where f=1/T and T is the repetition period ofthe pulses.

It was found that if the repetition frequency f is less than 20 Hz, theignition of the low and high current pulsed periodic discharges couldnot be achieved without an external pre-ionization. Without an externalpre-ionization the discharges have a random occurrence and appear in theform of contracted arc discharges. In the region of 20-100 Hz thedischarges can be periodically ignited without any externalpre-ionization because of the residual electrical conductivity of thedischarge gap. The residual conductivity is caused by residual plasmaremaining in the magnetic configuration from the previous pulse. If thepulse repetition frequency has a value of 20-100 Hz, the plasmaremaining in the magnetic configuration from the previous pulse has alow density and formation of arc discharges has a high probability,especially for the high current discharges. This is true for allmagnetic field parameters mentioned above in the paragraphs under a, b,c. If the magnetic field strength is less than 0.03 T the high currentquasi-stationary discharges cannot be started at all.

If the pulse repetition frequency is higher than 100 Hz the low and highcurrent, pulsed, periodic discharges have a stable arc-free operation ifthe magnetic field parameters are selected in accordance with that toldin the paragraphs a, b, c above.

The pulse repetition frequency is a decisive factor for achieving aselfsputtering regime. The selfsputtering regime for presence of asputtering gas such as Ar can be achieved already at a frequencysomewhat higher than 100 Hz. This is the argon assisted selfsputteringregime. Without sputtering gas the selfsputtering regime occurs atfrequency higher than 500 Hz.

After the start period it is possible to initiate the low and highcurrent EXB discharges in the residual plasma density remaining from theprevious pulse. In this case metal vapor is produced by theselfsputtering phenomenon and the plasma filling the magnetic trapcontains primarily ions of the target metal. The plasma flow from themagnetic trap contains preferably ions of the target metal as well. Theselfsputtering phenomenon can be produced for any type of cathodematerial if the low and high current discharges are used following eachother or generally by a DC discharge followed by a high currentdischarge, see FIGS. 3 a-7, and if the conditions mentioned in theparagraphs a-d above are fulfilled. The selfsputtering regime is highlyimportant for such applications as directional etching or cleaning ofwork pieces surface by metal ions for increasing the adhesion ofdeposited layers or for filling high-aspect-ratio trenches and viasencountered in microelectronic fabrication.

In the diagram of FIG. 7 a the selfsputtering phenomenon is illustrated.The low current discharge having a current intensity I₁ fills themagnetic trap near the cathode by a metal vapor. The ionization degreeof the gas and metal vapor by the low current discharge is negligiblecompared to those for the high current discharge and is not plotted inFIG. 7 a. The high current discharge ionizes the vapor and thesputtering gas. The plasma density increases from the value n_(min) upto value n_(max) during the period from t₂, t₃ up to t₄. Thecorresponding conductivity of the discharge gap increases from the valueσ_(min) up to the value σ_(max). After the ending time t₄ of the highcurrent discharge a period of plasma decay starts. It results in thatthe conductivity of the discharge gap decreases down to σ_(min). Thevalues n_(min) and σ_(min) depend on the pulse repetition period T,n_(max) and the plasma confinement properties of the magneticconfiguration, i.e. of the magnetic trap, provided that the parametersare within the ranges of the parameters indicated in the paragraphs a-dabove. The regime demonstrated by FIG. 7 can only be achieved by fillingthe magnetic trap with metal vapor produced by low current dischargeshaving the amplitude I₁. In this case the presence of gas is necessaryjust to start the discharges.

The method described herein comprising metal plasma production byproducing a metal vapor using magnetron sputtering and a followingionization of the produced vapor by pulsed discharges in crossed fieldshas some similarities to the RF-method described above. In that methodmetal plasma fluxes are produced by low current stationary EXBdischarges in magnetron magnetic configuration for sputtering atoms in amoderate pressure, e.g. of 1-100 mTorr, producing a low-density plasma.In that case the plasma is produced by an RF-induction coil mountedinside the deposition chamber. The electron density produced ininduction plasmas is of the range of 10¹⁷-10¹⁸ m⁻³. The drawbacks of theRF-method of metal plasma production include the complexity of theRF-ionization technique and the required high pressure of the sputteringgas, which as well is used for producing the low-density plasma.

Trap dimensions and metal vapor expansion speed define the time requiredfor filling the magnetic trap with metal vapor. The characteristic metalvapor expansion speed can be obtained from the energy distribution ofthe sputtered atoms. The energy distribution of the sputtered atomsaccording to linear collision cascade theory is described by theThompson formula, which was originally derived for energies of thekeV-range. Later, experiments confirmed that this formula is valid downto the eV-range, see H. Oechsner, “Energieverteilungen bei derFestkörperzerstäubung durch Ionenbeschuss”, Zeitschrift für Physik A,No. 238, 1970, pp. 433-451. For different metals the characteristicmetal vapor characteristic expansion speed is of the order of magnitudeof 10³-3·10³ m/s.

Furthermore, it was found that the characteristic height h, see FIGS. 1c, 1 f, of the magnetic trap or confinement region should be of theorder of the target diameter D for a planar circular geometry or of thesmaller dimension D of a rectangular cathode. The dimensions D and hdefine the power dissipation volume inside of magnetic trap.

Practically, the duration (t₂−t₁) of the first period in the pulses forthe low current discharge is equal to the time of filling the powerdissipation volume inside the magnetic trap by a metal vapor. Theduration should be β₁D, where the constant β₁ is measured in μs/cm andhas a value in the range of 0.1-3 μs/cm and D is measured in cm. Theduration (t₄−t₃) of the period for the high current discharges in thepulses depends on the dimension D and h as well and has a value β₂D,where the constant β₂ is measured in μs/cm and has a value in the rangeof 0.1-1 μs/cm and D is measured in cm.

The second periods of the pulses for the high-current discharges canfollow directly exactly after the first periods of the pulse for thelow-current discharge as shown by the diagram of FIGS. 3 a, 4 and 7 b.These second periods can also start some time Δ=(t₃−t₂) after the endsof the preceding first periods as shown by the diagram of FIG. 5. Thevalue of this delay time Δ depends on the required ionization rate ofthe metal vapor blob and is of the magnitude of order Δ=cD, where c is aconstant, measured in s/cm, and has a value in the range of 5·10⁻⁸-10⁻⁶s/cm and D is measured in cm as above.

The production of the metal plasma can, using the method as describedabove comprising pulses having two different current levels, be achievedalso by producing continuously a flow of metal vapor by a DC dischargeand accompanying it by pulsed high current ionizing quasi-stationarydischarges, see the diagrams of FIGS. 6 a, 6 b. In this case therepetition period T of the pulsed discharges is defined by expansionspeed of the metal vapor and by the dimensions of the magnetic trap. Therepetition period of the high current discharge is equal to the sum of alow current pulse duration of β₁D, as defined above, where the constantβ₁ is measured in μs/cm and has a value in the range of 0.1-3 μs/cm, andthe high current discharge pulse duration β₂D defined above, where theconstant β₂ is measured in μs/cm and has a value in the range of 0.1-1μs/cm.

As can be seen in the diagrams of FIGS. 3 a-7, the discharges arepreferably produced so that in each pulse or pulse portion the currentas a function of time has a rectangular shape.

Furthermore, the discharges are preferably produced so that in the firstperiods, for the pulses shown in FIGS. 3 a-5, the driving currentbetween the anode and the cathode is μ₁S, where μ₁ is a constantmeasured in A/cm² having a value in the range of 0.1-1 A/cm², and S isthe area of the active surface of the cathode measured in cm². Also, thedischarges are also preferably produced so that in the second periodsfor the pulses shown in FIGS. 3 a-5 and in the high current pulses shownin FIG. 6 b, the driving current between the anode and the cathode isμ₂S, where μ₂ is a constant measured in A/cm² and has a value in therange of 1-10 A/cm² and S is the area of the active surface of thecathode measured in cm².

The magnetrons including rotating magnets have to be consideredseparately. For calculation of the required values of the low and highcurrent pulses the sputtering area of the cathode for a fixed magnet hasto be chosen. The sputtered area is measured in cm². The coefficientsfor the low and high current pulses are equal to the coefficients forthe magnetron configuration according to the schematic of FIG. 1 c,which is chosen as the basic configuration. For calculation of pulsedurations the characteristic dimension D, see FIG. 1 h, has to be takenas the dimension of the sputtered area for a fixed magnet in thedirection coinciding with the direction N-S inside the permanent magnet.

In the chamber in which discharges are made a mixture of sputtering andreactive gases can exist at a pressure of preferably 10⁻¹⁰-10⁻² Torr.

In FIGS. 8 a, 8 b and 8 c electrical circuit diagrams of devices forproducing of metal vapor and the ionization thereof according to themethod described above are shown. The devices for performing the methodof preferably gas or gas-metal or preferably metal plasma productioncomprise four main parts, see FIGS. 8 a-8 b:

1. the magnetron sputtering cathode 1 or C,

2. a pulsed or DC power supply for achieving sputtering of the cathode,

3. a pulsed power supply for ionization of gas and metal vapor,

4. a timer for coordination of the operation of the power supplies.

The magnetron sputtering cathode 1, C is of the balanced or unbalancedtype or a combination of a cathode having a balanced magneticconfiguration and an electromagnetic coil producing an additionalmagnetic field, as described above. The DC power supply powers themagnetic coil 5. The integral magnetic field is of the unbalanced or ofthe cusp-shaped configuration, see FIGS. 1 d and 1 f. If the magnetronmagnetic configuration is of balanced type the maximum value of theradial component of the magnetic field at the sputtering surface ofcathode is in the range of 0.07-0.3 T. If the unbalanced magnetronmagnetic configuration is used, the maximum value of the radialcomponent of the magnetic field at the sputtering surface of the cathodeis in the range of 0.04-0.3 T. If the cusp-shaped axially symmetricmagnetic configuration is used the maximum value of the radial componentof the magnetic field at the sputtering surface of cathode is in therange of 0.04-0.3 T.

In FIG. 8 a a diagram of an electrical circuit is shown having twopulsed power supplies connected in parallel with each other andconnected to the discharge device, i.e. to the magnetron sputteringcathode 1, C and the anode A. The anode of the discharge can be thewalls of the vacuum chamber, which is then connected to ground, or aspecially designed anode, which can have an electric potential separatefrom the ground or have the ground potential. A first power supply PS-1produces pulses for sputtering the target, i.e. the low-current part ofthe discharges. A second power supply PS-2 produces pulses forionization of the sputtered metal vapor and sputtering and reactivegases, i.e. the high-current part of the discharges. The timer 11produces double triggering pulses. The time intervals between thetriggering pulses and the repetition frequency thereof are variable.R_(AC) is the characteristic impedance of the discharge gap, i.e. of thepath between anode A and cathode 1, C.

In the circuit diagram of FIG. 8 b instead a system comprising only onepulsed power supply having a variable impedance is shown. The timer 11produces double triggering pulses as described above.

In FIG. 8 c the electric wiring of a system having one pulsed powersupply combined with a DC power supply is shown. The timer here producesonly single triggering pulses having a variable repetition frequency.

The detailed circuit illustrated in FIG. 9 corresponds to that shown inFIG. 8 a. The circuit comprises the two pulsed power supplies PS-1, PS-2connected in parallel to each other, and each power supply based on aCL-circuit or CL-oscillator. Each power supply comprises a capacitor C₁,C₂ connected in parallel to a charger circuit 13 and diodes D₁, D₂. Oneterminal of the capacitors is connected to the anode A through aninductance L₁, L₂ and a switch T₁, T₂. The inductances L₁ and L₂ areused for limiting the discharge currents. The L₁ inductance is as highas necessary for producing the low current sputtering pulses. The L₂inductance is as low as necessary for producing the high currentionizing pulses. Thyristors are used as switches T₁, T₂. In principleany type of fast, high current switches are suitable. The timer 11produces double pulses for starting the pulsed discharges, e.g. as shownin FIG. 4. The chargers 13 are of any type pulsed charger. Thecapacitors C₁ and C₂ are charged during the time between the sputteringand ionizing processes. The diodes D₁, D₂ short-connect the capacitorsC₁, C₂ for preventing reverse polarity pulses. Reverse polarity pulsescan appear if the characteristic impedance R_(AC) of the discharge gapis too low.

The detailed circuit illustrated in FIG. 10 corresponds to that shown inFIG. 8 b. The circuit has a single pulsed power supply of the sameCL-type as used in FIG. 9. However, a limitation of the dischargecurrent is achieved by a resistor R which is connected in series withthe switch T₁ and the inductance L₁ of the power supply and can beshort-connected by a thyristor switch T₃ connected in parallel with theresistor, after a certain time period, necessary for vapor production.The timer 11 produces double pulses provided to the switches T₁ and T₃to give pulses as shown in e.g. FIG. 4.

The detailed circuit illustrated in FIG. 11 corresponds to that shown inFIG. 8 c. The circuit has a single pulsed power supply of the sameCL-type as used in FIG. 9 and a DC power supply connected to the anodeand cathode through a diode D₃. The timer produces single pulses forgenerating discharge pulses as shown in FIG. 6.

FIGS. 12 a and 12 b are schematic cross-sectional views of plasmasources utilizing discharges in crossed electric and magnetic fields forgas or gas and metal or metal plasma production. As an injector of metalvapor into the ionization region a planar magnetron sputtering cathodeis used.

In FIG. 12 a the unbalanced magnetron magnetic configuration of thesecond type as indicated in FIG. 1 c is shown. The permanent magneticsystem 21 is thus the unbalanced type, type 2, and is located at therear side of the cathode 23. The magnetic system has to create amagnetic field having a maximum intensity 0.3 T of its radial componentat the active or front surface of the cathode 23. A mechanical system 22is arranged for adjusting the magnetic field intensity in the centralfront region 5 at the front surface of the cathode. The limits for themagnetic field adjustment are 0.04 T and 0.03 T. The precision of themagnetic field adjustment is 0.005 T.

The cathode 23 is a circular or rectangular planar magnetron sputteringcathode of conventional type. The anode 24 of the EXB discharge includesthe sidewalls of the sputtering chamber which comprise a cylindrical orrectangular tube 35 and a planar diaphragm 32 including an outlet 34 forthe plasma flow. The outlet 34 has the shape of a contracting nozzle.The inner surface of the nozzle 34 is configured as a magnetic fieldsurface. The cross-section of the nozzle 34 as taken perpendicularly tothe axis of the plasma source has a circular shape for a circularcathode 23 or a rectangular shape for a rectangular cathode. The anode24 is connected to ground as indicated at 31.

The cathode 23, the anode 24, and the permanent magnetic system 21 areall water-cooled. The water inlet and outlet openings are shown at 30.An electrical insulator 28 is arranged between the anode 24 and thecathode 23. A gas inlet opening 29 is provided in the cylindrical tube35 for supplying the gas into the anode vessel.

The power supply 26 is arranged according to one of FIGS. 8 a-FIG. 11.The repetition frequency of the applied pulses is variable from 100 Hzup to 20 kHz. The power supply 26 has to generate, for a resistive loadof 1 ohm, pulses having peak voltages in the range of 0.4-4 kV. Thepower supply 26 has to operate with a resistive load of 2·10⁻³ (cm⁻²) Sohm. The area S is the area of the sputtered cathode surface measured incm². The rise time of the current pulse from 0 A up to the peak currentis 10⁻⁵ s in a resistive load of 0.3 ohm. The power supply 26 isconnected to the plasma source by a coaxial cable 27. The coaxial cableconnection is used for reducing the inductance of the line between thepower supply and the plasma source. It allows that the required risetime of the ionizing discharge current is achieved. The rise time of theionizing discharge current has to be less than the time of flight ofmetal vapor blobs across the magnetic field configuration 25 at theactive front side of the cathode 23.

In the schematic cross-sectional view of FIG. 12 b the magnetronmagnetic configuration indicated in FIGS. 1 d and 1 f is shown in somemore detail. These magnetic configurations are obtained by a permanentmagnetic system of the balanced type as shown in the schematic of FIG. 1b and by arranging an unbalancing electromagnetic coil 36. Otherwise,the design of the plasma source is as similar to that illustrated inFIG. 12 a.

The magnetic field intensity created by the permanent magnetic system 21and the precision of the field adjustment are identical to thosedescribed with reference to FIG. 12 a. The electromagnetic coil 36creates a magnetic field having an intensity sufficient to obtain, atthe center of the sputtering cathode 23 surface, a field intensity of upto 0.15 T. The magnetic field generated by the electromagnetic coil 36is variable from 0 T up to the maximum intensity with a 0.001 T.

The plasma sources according to FIGS. 12 a and 12 b are connected to avacuum vessel 33.

The plasma sources of FIGS. 12 a and 12 b operate as follows. Theinitial magnetic field intensity is 0.15 T. The sputtering and ionizinggases are supplied into the anode vessel 24 through the gas inlet 29.The initial operating pressure is in the range of 10⁻²-10⁻⁴ Torr. Afterthe required operating pressure has been achieved the power supply 26 isswitched on. The power supply 26 supplies the low intensity current andhigh intensity current pulses to the plasma source. The initialrepetition frequency of the applied pulses is 100 Hz. After thedischarge has been ignited the magnetic field intensity and therepetition frequency of the pulses are adjusted to obtain dischargeswithout any concentrated arc formation. If the self-sputtering mode ofplasma source operation is desired, the repetition frequency of thepulses is increased with a simultaneous reduction of the operatingpressure. The repetition frequency of the pulses is increased up to thevalue when the plasma source can operate without operating gas. Thebasic (operating) pressure has to be less then 10⁻⁴-10⁻⁵ Torr. In thisregime the plasma source produces only metal plasma.

While specific embodiments of the invention have been illustrated anddescribed herein, it is realized that numerous additional advantages,modifications and changes will readily occur to those skilled in theart. Therefore, the invention in its broader aspects is not limited tothe specific details, representative devices and illustrated examplesshown and described herein. Accordingly, various modifications may bemade without departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents. It istherefore to be understood that the appended claims are intended tocover all such modifications and changes as fall within a true spiritand scope of the invention.

1-36. (canceled)
 37. A method for producing plasma from a metal and/or agas in a chamber and between a anode and cathode of said metal ormetals, said chamber having crossed electric and magnetic fields andsaid gas at a low pressure, said method comprising: generating periodicrepeated double-pulse electrical discharges wherein each double-pulsedischarge comprises first and second pulsed electrical dischargesbetween the anode and the cathode to produce metal plasma, wherein saidfirst pulsed electrical discharge occurs during a first time period andis generated by a low electrical current supplied by a first powersupply, said low electrical current passing between the anode andcathode for achieving a sputtering discharge producing a metal vapor bymagnetron sputtering, and wherein said second pulsed electricaldischarge occurs during a second time period and is generated by a highelectrical current supplied by a second power supply, said highelectrical current passing between the anode and cathode for ionizingthe gas and the metal vapor, said high electrical current being higherthan said low electrical current, wherein during the second time periodsthe driving current between the anode and the cathode is μ₂S, wherein μ₂is measured in A/cm² and has a value in the range of 1-10 A/cm² and S isthe active surface of the cathode measured in cm², and wherein saidfirst time period is longer than said second time period.
 38. A methodaccording to claim 37, wherein said double-pulse discharges are producedwith a frequency of 100 Hz-20 kHz.
 39. A method according to claim 37,wherein during the first time period when the discharges are low thedeposition rate increases with increasing discharge current, and duringthe second time period when the discharges are high the deposition ratedecreases with increasing discharge current.
 40. A method according toclaim 37, wherein said sputtering discharges in said first time periodsare low intensity current quasi-stationary discharges and saidionization discharges in said second time periods are high intensitycurrent non-quasi-stationary discharges in crossed electric and magneticfields.
 41. A method according to claim 37, wherein during the firsttime periods the driving current between the anode and the cathode isμ1S, where μ1 is measured in A/cm² and has a value in the range of 0.1-1A/cm² and S is the area of the active surface of the cathode measured incm².
 42. A method according to claim 37, wherein during the first timeperiods have a duration β1D, where β1 is measured in μs/cm and has avalue in the range of 0.1-3 μs/cm and D is the diameter of a circularcathode or the smaller dimension of a rectangular cathode measured incm.
 43. A method according to claim 37, wherein said second time periodshave a duration of β2D, where β2 is measured in μs/cm and has a value inthe range of 0.1-1 μs/cm and D is the diameter of a circular cathode orthe smaller dimension of a rectangular cathode measured in cm.
 44. Amethod according to claim 37, characterized by the additional step ofproviding in the chamber a magnetron magnetic configuration of balancedtype having a maximum value in the range of 0.07-0.3 T of the radialcomponent of the magnetic field at the active surface of the cathode.45. A method according to claim 37, characterized by the additional stepof providing in the chamber a mixture of sputtering and reactive gasesat a pressure in the range of 10⁻¹⁰-10⁻² Torr.
 46. A method according toclaim 37, characterized by the additional step of providing in thechamber a magnetron magnetic configuration of unbalanced type having amaximum value in the range of 0.04-0.3 T of the radial component of themagnetic field at the active surface of the cathode.
 47. A methodaccording to claim 37, characterized by the additional step of providingin the chamber a magnetron magnetic configuration of the type having acusp-shaped axially symmetric magnetic configuration having a maximumvalue in the range of 0.04-0.3 T of the radial component of the magneticfield at the active surface of the cathode.
 48. A method according toclaim 37, wherein the first pulse discharge is separated from the secondpulse discharge by a delay.
 49. A method according to claim 48, whereinno driving current is produced during said delay.
 50. A method accordingto claim 49, wherein said delay has a duration t=cD, where c is measuredin s/cm and having a value in the range of 5*10⁻⁸-1*10⁻⁶ s/cm and D isthe diameter of the cathode measured in cm.
 51. A method according toclaim 38, wherein said double-pulse discharges are produced with afrequency of 0.5-2 kHz.
 52. A device for producing plasma flows of ametal and/or a gas comprising: a chamber for maintaining a gas at a lowpressure; an anode and a magnetron sputtering cathode, the cathodecomprising a metal or metals for metal plasma production, a magnetassembly for making electric discharges in crossed electric and magneticfields; a power supply assembly for periodically producing electricdischarges between the anode and the cathode, said power supply assemblycomprises first and second power supplies, wherein said first powersupply delivers to said anode and cathode first pulses low electriccurrent driving pulses for producing a gas/metal vapor by magnetronsputtering of the cathode and said second power supply delivers to saidanode and cathode second high electric current driving pulses forionizing the gas and/or metal vapor produced in the chamber, wherein thedriving current of said second pulses between the anode and the cathodeis μ2S, wherein μ2 is measured in A/cm2 and has a value in the range of1-10 A/cm2 and S is the active surface of the cathode measured in cm2,wherein the driving current of said second pulses is higher than thedriving current of said first pulses, and wherein said first pulses havea longer duration than said second pulses; and a timer for periodicallytriggering pulses to the first and second power supplies such that saidthe first and second pulse discharges are provided as double-pulseelectrical discharges, comprising a first pulse for a sputteringdischarge and second pulse for an ionizing discharge, wherein the firstpulse ends before the second pulse begins.
 53. A device according toclaim 52, characterized in that at least one of the power supplies isdimensioned to generate for a resistive load of 1 ohm pulses having peakvoltages in the range of 0.4-4 kV.
 54. A device according to claim 52,wherein said power supplies comprise a capacitor connected in parallelto a charger circuit.
 55. A device according to claim 52, wherein duringthe first pulses when the discharges are low the deposition rateincreases with increasing discharge current, and during the secondpulses when the discharges are high the deposition rate decreases withincreasing discharge current.